Prosocial decisions can be difficult because they often involve personal sacrifices that do not generate any direct, immediate benefits to the self. The current study used functional magnetic resonance imaging (fMRI) to understand how individuals decide to provide support to others. Twenty-five participants were scanned as they completed a task in which they made costly decisions to contribute money to their family and noncostly decisions to accept personal monetary rewards. Decisions to contribute to the family recruited brain regions involved in self-control and mentalizing, especially for individuals with stronger family obligation preferences. Psychophysiological interaction (PPI) analyses revealed that individuals with stronger family obligation preferences showed greater functional coupling between regions involved in self-control and mentalizing with the ventral striatum, a region involved in reward processing. These findings suggest that prosocial behavior may require both social cognition and deliberate effort, and the application of these processes may result in greater positive reinforcement during prosocial behavior.